THE IMPORTANCE OF TRANSMISSION-BLOCKING IMMUNITY IN THE CONTROL OF INFECTIONS BY APICOMPLEXAN PARASITES

Transmission-blocking immunity may have great potential for use in the control of diseases caused by apicomplexan parasites. In this review I will describe our work on the application of transmission-blocking i mmunity to the control of the Eimeria parasite and compare our results to those working on transmission-blocking immunity against Cryptospor idium and Plasmodium. Eimeria causes the disease known as coccidiosis in domestic animals. Coccidiosis is particularly problematic in the ch icken industry, mainly due to the crowded rearing conditions under whi ch chicks are raised. In our work we identified, isolated and characte rized 3 major gametocyte antigens (230 kDa, 82 kDa and 56/54 kDa) of E imeria maxima. We used these native glycoproteins to immunize laying h ens that, via the egg yolk, provide large amounts of transmission-bloc king maternal antibodies to offspring chicks. We demonstrated that hat chlings from immunized hens shed 60-80% fewer oocsyts (i.e. the infect ive stage of the life-cycle of Eimeria) than those from control hens. Such a reduction in oocyst output acts to significantly reduce parasit e numbers in the litter of chicks raised in floor pens. This reduction in oocyst output is comparable to that seen using the most effective coccidiostat drugs and is probably sufficient to control coccidiosis u nder field conditions. Based on our results together with those of oth er groups working on transmission-blocking immunity against Cryptospor idium and Plasmodium, it appears that this immunological approach hold s great promise for the control of apicomplexan parasites that cause d iseases in both animals and man. (C) 1997 Australian Society for Paras itology, Published by Elsevier Science Ltd.